1. Field of the Invention
This invention relates to a toner used in image forming processes for making electrostatic latent images into visible images, such as electrophotography, and a toner used in toner jet recording.
2. Related Background Art
In recent years, machinery making use of electrophotography has begun to be used in printers for computer data output, facsimile machines and so forth in addition to copying machines for copying original images. Accordingly, machines are severely sought to be more compact, more light-weight, more high-speed and more high-reliability, and have come to be constituted of simple components in various aspects. As the result, the performance demanded of toners has come so higher that any superior machines are not set up unless improvements in performance of the toners can be achieved.
In particular, in respect of energy saving and office space saving, machines such as printers are required to be made more compact. On that occasion, containers which hold toners therein are also necessarily required to be made compact, and a low-consumption toner is required that enables many-sheet printing in a small quantity, i.e., that can manage the printing of the same images in a smaller quantity of toner.
Techniques are disclosed in which the particle shape of toner is made close to spherical shape by production processes such as spray granulation, solution dissolution, and polymerization (e.g., Japanese Patent Applications Laid-open No. H3-84558, No. H3-229268, No. H4-1766 and No. H4-102862). These techniques, however, all require large-scale equipment for the production of toners. This not only is undesirable in view of production efficiency, but also has not achieved any sufficient reduction of toner consumption.
Techniques are also disclosed in which toners produced by pulverization are made to undergo thermal or mechanical impact to modify the shape and surface properties of particles (e.g., Japanese Patent Applications Laid-open No. H2-87157, No. H10-97095, No. H11-149176 and No. H11-202557). However, modifying the particle shape of toner by these methods can not be said to be sufficient for the reduction of toner consumption, and also has brought about difficulties such as a lowering of developing performance in some cases.
It is commonly known to add small-particle-diameter inorganic fine particles to toner base particles for the purpose of controlling chargeability, fluidity and so forth of toners to achieve good developing performance.
In toners to which such small-particle-diameter inorganic fine particles are added, it has been ascertained that the small-particle-diameter inorganic fine particles come to stand buried in surface portions of toner base particles because of, e.g., a stress applied between a toner and a carrier when the toner is used as a two-component developer, a stress applied from a developing blade and a developing sleeve when the toner is used as a one-component developer, an impact against inner walls of a developing assembly and against a toner agitation blade, and a mutual impact between toner particles.
In order to make the small-particle-diameter inorganic fine particles less buried, it is effective to use large-particle-diameter inorganic fine particles in combination, as disclosed in Japanese Patent Applications Laid-open No. H4-204751, No. H5-346682, No. H6-313980, No. H6-332235 and No. H7-92724.
The large-particle-diameter inorganic fine particles have an effect as a spacer, and hence they prevent toner base particle surfaces to which the small-particle-diameter inorganic fine particles have adhered, from coming into direct contact with the carrier, developing blade, developing sleeve, developing assembly inner walls, toner agitation member and other toner to lessen the stresses. This makes the small-particle-diameter inorganic fine particles kept from being buried in the surface portions of toner base particles, and brings achievement of longer lifetime of toners.
Japanese Patent Application Laid-open No. H4-204751 discloses a toner containing hydrophobic fine silica particles and hydrophobic fine titanium oxide particles or hydrophobic fine aluminum oxide particles, which is a toner characterized in that the hydrophobic fine titanium oxide particles or the hydrophobic fine aluminum oxide particles have peaks at 10 to 20 nm and 30 to 60 nm in primary particle diameter.
Japanese Patent Application Laid-open No. H5-346682 discloses a toner characterized in that an inorganic fine powder having a BET specific surface area of less than 80 m2/g and treated with a silicone oil and an inorganic fine powder having a BET specific surface area of 80 m2/g or more and treated with a silane coupling agent are blended.
Japanese Patent Application Laid-open No. H6-332235 discloses a toner for electrophotography which comprises toner base particles and at least two types of external additives, and is a toner for electrophotography which is characterized in that particles of 5 μm or smaller are present in a proportion of 1 to 8% by volume in particle size distribution of toner base particles, that a first external additive has an average particle diameter of 0.1 to 0.5 μm in number base of primary particles, and that a second external additive has an average particle diameter of 20 nm or less in number base of primary particles and is hydrophobic.
Japanese Patent Application Laid-open No. H7-104501 discloses a proposal of a toner making use of hydrophobic fine silica particles of 15 to 20 nm in particle diameter and hydrophobic fine silica particles or alumina fine particles of 13 nm or less in particle diameter.
However, because of the addition of two types of hydrophobic fine particles different in particle diameter, these toners have had problems in respect of mixability of the both and dispersion on the surfaces of toner base particles, and had insufficient development durability and charging stability.
Japanese Patent Application Laid-open-No. H6-313980 discloses a developer characterized in that inorganic fine particles have, in their number primary particle diameter distribution curve, i) a maximum value of number proportion at each of a primary particle diameter x (nm) (where 20≦x≦50) and a primary particle diameter y (nm) (where 3x≦y≦6x) and ii) 10% by number or less of number proportion in the primary particle diameter (x+y)/2 (nm), have a value of X/Y within the range of from 0.5 to 2.0 where the number proportion of inorganic fine particles on the side of small particle diameter which have a primary particle diameter of less than (x+y)/2 (nm) is represented by X % by number and the number proportion of inorganic fine particles on the side of large particle diameter which have a primary particle diameter of (x+y)/2 (nm) or more by Y % by number, and have a value of z/x of from 150 to 400 where the volume-average particle diameter of toner base particles is represented by z (nm).
However, in this inorganic fine particles, the peak of the primary particle diameter on the side of small particle diameter in the number primary particle size distribution is as relatively large as 20 nm or more, and moreover a peak is also present on the side of large particle diameter. Hence, when calculated on the basis of weight, it follows that the large-particle-diameter inorganic fine particles are present in a very large number with respect to the small-particle-diameter inorganic fine particles, bringing about problems on fluidity and chargeability.
Japanese Patent Applications Laid-open No. H8-36316, No. 2000-56595 and No. 2002-23414 disclose, in a contact transfer assembly in which a bias is applied to a transfer member by a means for applying the bias and a toner held on a latent image bearing member, prepared by externally adding to and mixing in toner base particles at least two types of external additives different in average particle diameter, is transferred to a transfer medium, a transfer assembly which has defined the relationship between the loose apparent density of the toner and the hardness of the transfer member. However, the respective two types of external additives different in average particle diameter, used here, have separately been hydrophobic-treated, and hence the both differ in their agglomerative properties and readiness of dispersion on toner base particle surfaces, and it has been difficult to disperse the both uniformly on the surfaces of toner base particles.
A method is also employed in which toner base particles are incorporated with a wax for the purpose of improving releasability of the toner. Toners the base particles of which are incorporated with two or more types of waxes in order to bring out the effect of addition of the wax over the range of from a low-temperature region to a high-temperature region are disclosed in, e.g., Japanese Patent Publication No. S52-3305 and Japanese Patent Applications Laid-open No. S58-215659, No. S62-100775, No. H4-124676, No. H4-299357, No. H4-362953 and No. H5-197162. However, even when the toner base particles are incorporated with such waxes, not only no sufficient fixing performance and releasability may be obtained, but also faulty images due to faulty cleaning have occurred in some cases.